The human body has many regions in which pressure differences cause matter to move. For example, the human heart pumps blood through the body. Muscles around the alimentary canal apply a pressure to the canal, which moves food from the mouth into the stomach.
Monitoring pressures and motion in the human body can provide important information about the function of the human body and can be used to detect disorders and diseases or can be used to control a recovery from a disease.
Optical devices for monitoring pressures within a body lumen are now being developed. Such optical devices are typically very narrow and consequently do not cause too much discomfort to a patient. The optical devices may comprise an optical fibre Bragg grating, which has an optical response that depends on a strain of the Bragg grating. The strain of the Bragg grating is applied by a “squeezing” force in the vicinity of the Bragg grating and the resultant increase in strain shifts a wavelength of an optical response to a longer wavelengths range.
However, important information directly characterising a longitudinal motion, such as a motion of bolus along the oesophagus effected by muscles of the oesophagus, or longitudinal motion of the oesophageal wall itself, cannot be provided in a convenient manner using known devices.